1. Field of the Invention
This invention concerns a dilution pipetter and, more specifically, it relates to a dilution pipetter for distributing a liquid sample each by a small volume to a plurality of reaction tubes respectively for dilution. The dilution pipetter of this invention is useful as, e.g., an element of a clinical chemistry analyzer which is used to conduct a number of reactions for small quantities of a liquid sample such as serum of the warm blooded animals including humans.
2. Description of the Prior Art
A dilution pipetter 1 as shown in FIG. 1 has heretofor been used [e.g., Simadzu Review, Vol. 38 No. 2 99-111 (1981)]. In the pipetter 1, liquid sample S is sucked from a sample cup 9 into a sample probe 3 by the sucking operation of a plunger pump 6 of small diameter while turning a first switching valve 5 to a normally closed (NC) position. Upon distributing the liquid sample S, the sample probe 3 is moved to a reaction tube 10 and then a diluent D is sucked through a diluent suction probe 2 by the sucking operation of the plunger pump 6 while turning the first switching valve 5 to a normally opened (NO) position. Then, the diluent D is sent to the sample probe 3 by the discharging operation of the plunger pump 6 to thereby push out the sample S in the sample probe 3 while turning the first switching valve 5 to the NC position. The diluent D is supplied through a diluent discharge probe 4 by the sucking operation of a plunger pump 8 of large diameter while turning a second switching valve 7 to the NC position and by the subsequent discharging operation of the plunger pump 8 while turning the second switching valve 7 to the NC position. Usually, the diluent discharge probe 4 is disposed in adjacent with the sample probe 3 so that the diluent liquid D discharged from the probe 4 flows to the probe 3 in order not to leave a droplette of the sample S at the top end of the sample probe 3.
In a case of distributing the sample S over a plurality of reaction tubes 10, 10', . . . , a large amount of the sample S has to be sucked at first into the sample probe 3. However, it takes a considerably long time for sucking such a large amount of liquid in the conventional pipetter since the plunger diameter of the pump 6 is small and thus needs a longer plunger stroke. Although the sucking time may be shortened by enlarging the plunger diameter to decrease the plunger stroke, this will lead to the reduction in the accuracy for the distributional ejection of the sample.